Monopile platforms are rather slim structures which are sensitive to wave loadings and the natural period of them are within the range of sea waves' periods. Therefore, suitable dynamic analysis and wave modeling for these platforms is necessary. There are two methods for analyzing such flexible structures under wave loading, i.e., deterministic and random methods. In deterministic method, a regular wave representing the sea state is used while random analysis considers irregular wave including spectral and time history analysis. A comprehensive research has been carried out by applying the above mentioned methods for several monopile platforms to evaluate the validity of these methods. Results show that time history random method has the most reliable responses because of accurate modeling of waves and considering nonlinearities in the analysis. However, spectral method accuracy is acceptable if inertia term of wave loading is dominated and natural period of platform is far from wave period. Deterministic method can be used when platform has high rigidity.